Layered electron beam columns are described in U.S. Pat. Nos. 7,045,794, 7,109,486, 7,332,729, and 7,335,895, now assigned to the assignee of this disclosure, and in U.S. Pat. Nos. 8,003,952, 8,106,358, 8,110,801, and 8,115,168, assigned to the assignee of this disclosure. A layered electron beam column is composed of a stack of layers of insulating materials such as ceramic, glass and undoped semiconductor. Each layer supports a respective miniature component capable of extracting, accelerating, collimating, focusing, blanking, or steering, etc., an electron beam. The use of a layered electron beam column allows a scanning electron microscope (SEM) to be reduced in size from a room-sized instrument to a benchtop instrument. Scanning electron microscopes similar in size to a typical laser printer are now commercially available, for example, the model 8500 FT-SEM sold by Agilent Technologies, Inc., Santa Clara, Calif.
Energy dispersive spectroscopy (EDS) is described by Joseph Goldstein et al. in Chapter 7 of Scanning Electron Microscopy and X-ray Microanalysis, 3rd ed., (Springer US 2003). Energy dispersive spectroscopy can be used for material identification and quantification of the constituents of a sample. To uniquely identify a particular atomic species in a sample, at least two X-ray lines need to be identified. The electron beam energy needed to generate x-rays at at least two wavelengths from a given atomic species increases with atomic number. For example, to uniquely identify atomic species with atomic numbers greater than 14 requires an electron beam energy greater than 2 keV. Conventional SEMs use beam energies substantially greater than 2 keV, and can therefore offer full-spectrum EDS as an auxiliary feature. However, voltage maxima in the layered electron beam column of current layered electron beam column benchtop SEMs limit the electron beam energy to less than that needed to generate x-rays at multiple wavelengths from a full spectrum of atomic species. Consequently, current layered electron beam column benchtop SEMs offer only a part-spectrum capability.
Accordingly, what is needed is an SEM with a layered electron beam column that has a full-spectrum EDS capability.